Process for producing oxygen of high purity



4- G. .1. BOSHKOFF 1,985,763

PROCESS FOR PRODUCING OXYGEN OF HIGH PURITY Filed May 18,1935 2 Sheets-Sheet l fliqtl.

INVENTOR.

ATTORNEYS.

Dec. 25, 1934. J BQSHKOFF 1,985,763

PROCESS FOR PRODUCING OXYGEN OF HIGH PURiTY Filed May 18, 1955 2 Sheets-Sheet 2 I N VEN TOR.

Patented Dec. 25, 1934 I UNITED STATES PATENT OFFICE PROCESS FOR PRODUCING OXYGEN OF HIGH PURITY George J. Boshkoff, Buffalo, N. Y., assignor to The Linde Air. Products Company, New York, N. Y., a corporation of Ohio Application May 18, 1933, Serial No. 671,690

' Claims.

by it is substantially free from small amounts of hydrocarbons and other undesired gases ordina'rily present in the incomingair', which is employed as the raw material from which theoxygen is to be separated.

It is also an object to providej'a method of 20. operating gas separating apparatus with rectification chambers or columns so arranged that substantially pure oxygen is separated by fractional condensation and evaporation without being contaminated with undesired high boiling point materials and without interfering with the stability and operative balance in the cyclic operations taking place in the rectification columns or chambers.

Other objects of the inventiohwill in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the several steps andthe relation of one or more of such steps with respect to each of the others thereof,

which will be exemplified in the method hereinafter disclosed and the scope of the application ofwhich will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

Fig. 1 is a fragmentary vertical sectional view showing somewhat diagrammatically a rectification apparatus constructed in accordance with the invention; and

Fig. 2 is a similar view showing a modified arrangement in which the added column provided in accordance with the invention, is operated separately.

In the manufacture of oxygen for industrial use, it is customary to employ air as the raw material and to separate the oxygen .from the air in one or more stages by the rectification of liquid air, the atmospheric air having been compressed and cooled by heat exchangers and expanded in various stages by steps well known to the art. There are in air, as is well known, certain gas materials, of high boiling point which frequently comprise undesirable impurities in oxygen obtained in this manner. Also, where oxygen is to 5 be provided for industrial use, small amounts of certain hydrocarbons and other undesirable gases may be present as impurities. By the present invention, these high boiling point materials are separated from the liquid oxygen by steps which 10 do not require the input of any more power than is now customarily employed in the operation of the usual rectification cycle.

In the practice of the present invention, the step of rectifying the gaseous mixture in the low 15 pressure rectifying column or chamber is performed in two stages carried out successively. This is advantageously achieved by dividing the low pressure rectifying chamber or column into two parts and operating them in series. This 20 division preferably afiects what would ordinarily be the lower two-thirds of the low pressure rectifying column of a two-column rectifying apparatus.

Referring now to the drawings and particularly to Fig. 1, 10 denotes generally the high pressure column or'chamber of a rectifying apparatus into which the gaseous mixture to be separated is introduced in a cooled state through the conduit 11, the cooling being carried out in any well-known manner, for example, by means of expansion or passage through heat interchangers, or both. This column is also provided with suitable dephlegmating means, for example, perforated partitions 12. The lower end 13 of this column serves as a kettle in which liquid collects and boils, the more volatile products passing upwardly in the column. From this kettle the conduit 14 leads to a distributing head 15 disposed in the upper portion of a low pressure chamber or column 16 preferably disposed above the high pressure chamber 10. In the lower end of this second chamber is disposed a condenser 17 which serves to receive the volatile material arising from the chamber 10, a substantial portion thereof being condensed and returned to the chamber. From the upper end of this condenser a conduit 18 leads off the uncondensed material which is here utilized in the manner hereinafter more fully explained. The heat extracted by the condenser 17 in cooling the condensate returned to the high pressure chamber is supplied to vaporize the liquid which collects in the lower end of chamber 16. This second chamber also has suitable dephlegmating means, here represented as partitions 19 similar to those in the chamber 10.

To provide another chamber to be operated in series with the chamber 16, in accordance with the invention, a third chamber 20 is here shown as provided above the chamber 16. In the upper portion of this chamber is a distributing head 21, to which liquid condensate, caught on the partition or shelf 22 in the chamber 10, is supplied by means of a conduit 23 that communicates at its lower end with the chamber 10 just above the shelf. The chamber 20 is also provided with dephlegmating means, here shown as partitions 24, similar to those in chambers 10 and 16.

In order to vaporize the liquid which collects in the lower end of chamber 20 in a manner similar to that in chamber 16, a heating coil 25 is provided in this chamber and the uncondensed gaseous material led off by the conduit 18 supplied thereto through a branch connection 18. The liquid obtained by condensation in coil 25 is supplied by another conduit 26 to the distributing head 21. Gaseous material which is substantially pure oxygen is led off from the chamber 16 to chamber 20 through conduit 27, this conduit being provided with a branch 2'?" for bleeding off gaseous material when desired. It is also desirable to transfer gas material from the upper portion of chamber 16 to an intermediate point in chamber 20. The uncondensable gas materials which have a very low boiling point are preferably led OK the top of the chamber 20 by means of a conduit here indicated at 28;

In operation, when the gaseous mixture supplied to the chamber 10 through the conduit 11 is cooled compressed atmospheric air, liquid collects in the kettle 13 which becomes relatively rich in oxygen, since the more volatile constituents, such as nitrogen, are being continually boiled off and washed, the condensate being returned by counter washing or refluxing. The oiq'gen' content of the liquid which collects in the kettle 13 becomes relatively high, for examplefrom to 45%. While it is seen that the more volatile constituents, that is, the low boiling point constituents, are continually removed, the high boiling point constituents which include undesired impurities remain and are passed into the low pressure chamber 16 by way of conduit 14. y

In the chamber 16, the liquefied gas material of high oxygen content collects again in the lower end and is heated, whereby further volatile constituents are removed. A liquid of very high oxygen content, in consequence, results, but still includes the high boiling point impurities. The oxygen portion is here vaporized without carrying off any of the high boiling point impurities.

By operating the chamber 20 in series with the chamber 16, a gaseous material comprising substantially pure oxygen free from high boiling point impurities is withdrawn through the conduit 2'7 and is condensed by counter-current washing-so as to collect about the coil 25, substantially all the remaining volatile or low boiling point material being removed and withdrawn through the connection 28. Gaseous material is also conducted by conduit 27' from the upper portion of chamber 16 to a point near the upper portion of chamber 20; the oxygen content thereof, however, is substantially lower than the oxygen content of the liquid introduced into chamber 16 through conduit 14. In consequence,

substantially pure liquid oxygen may be withdrawn from the lower portion of this chamber through the withdrawal connection 29. A withdrawal connection 29' is advantageously provided for the lower end of chamber 16 in order to carry away when desired the high boiling point impurities which may collect.

In Fig. 2, a modified arrangement of apparatus for carrying out the process of the present invention is shown in which the divided low pressure chambers that are operated in series are shown as structurally separated. Here, a high pressure column or chamber is shown at 30, to which a cooled, compressed, gaseous mixture is supplied through a conduit 31. Thischamber has dephlegmating means 32 and a kettle 33 at the lower end, from which liquid comprising a high concentrateof oxygen is withdrawn through a. conduit 34 and supplied to a distributing head 35 in a low pressure chamber or upper column 36 of a two-column rectifying apparatus. This apparatus may be generally of conventional design, except that the other chamber is shorter, as it is the'lower two-thirds of the conventional upper chamber that is divided to provide a second low pressure chamber separated as indicated from that at 36, but arranged to be operated in conjunction therewith.

In the lower end of the upper chamber 36 is disposed a condenser 37 adapted to return condensate to the lower chamber 30. Uncondensed gas material is withdrawn through the conduit 38 and supplied to the heat transfer means dispos'ed in the lower end of the chamber 40. The upper chamber 36 also has dephlegmating means 39 and gas withdrawal connections 47 and 4'7 which communicate with intermediate points in the chamber 40.

Chamber 40 has a distributing head 41 and dephlegmating means 42, conduit 43 being arranged to lead condensate of relatively high nitrogen concentration from an upper shelf in the chamber 30 to the head 41. A conduit 46 leads from the lowerend of the heat transfer means 45 to supply gas material, in this case condensate, to the head 41. A conduit 48 leads from the top of the chamber 40 to convey away uncondensed, low boiling point gas materials.

In operation, the apparatus shown in Fig. 2 operates similarly to that shown in Fig 1. In consequence, a liquid having an increased concentration of oxygen collects in the kettle 33 along with the undesired high boiling point impurities.

In the upper chamber 36, a liquid collects about the condenser 37, which is substantially pure oxygen, but for the high boiling point impurities which are contained therein. The oxygen content is here vaporized and the gaseous oxygen and volatile materials are conveyed by conduits 47 and 47' into the chamber 40, where the low boil-' ing point materials are separated out and conveyed away through the conduit 48, leaving a liquid to collect about the heat transfer means 45 which is substantially pure liquid oxygen free of high boiling point This is withdrawn when desired through the conduit 49.

Since certain changes in carrying out the above process which embody the invention, may be made without departing from its scope, it is intended that all matter contained in the .above descrip-- tion or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. The process of producing oxygen substantially free'from undesired materials which comprises first producing a liquefied gaseous mixture rich in oxygen together with any undesired high boiling point material present, and then rectifying said liquefied gaseous mixture in two low pressure stages at successively lower pressures, in the first stage of which the liquefied gaseous mixture refluxes vapors of said mixture, which vapors are produced by heat exchange when producing said mixture, passing solely gas material directly from the first low pressure stage to the second low pressure stage and in said second low pressure stage refluxing with a liquid produced by the liquefaction of vapors remaining from the production of said liquefied gaseous mixture, and collecting oxygen in the liquid phase substantially free, from the undesired materials.

2. The process of producing oxygen substantially free from undesired materials from compressed and processed atmospheric air which comprises first liquefying and rectifying at a relatively high pressure the gaseous mixture to provide material in the liquid phase relatively rich in oxygen and containing undesired high boiling point material, and then rectifying the material rich in oxygen in two successive stages, in the first stage of which an intermediate pressure is maintained and the distillate refluxed solely with liquid produced by said first rectification while oxygen in the gas phase is withdrawn therefrom together with any low boiling material present and passed directly to said second stage, and in said second stage maintaining a relatively low pressure and refluxing with another product rich in nitrogen from said first rectification, said product having been substantially liquefied, while withdrawing oxygen substantially free from undesired materials.

3. The process of producing oxygen substantially free from undesired materials which comprises first rectifying in a single main stage at a relatively high pressure a liquefied gaseous mixture obtained from the atmosphere to provide material in the liquid phase rich in oxygen together with all undesired high boiling point material present and a gas rich in nitrogen, collecting at another point in said main stage a liquid relatively poor in oxygen, and then, rectifying said material rich in oxygen in two successive auxiliary stages, in the first of which an intermediate pressure is maintained whilevaporsproduced by heating said liquid rich in oxygen are refluxed with the liquid rich in oxygen transferred from said first rectification, withdrawing oxygen in the gas phase from the first of said auxiliary stages together with any low boiling point material present and passing the same directly to said second auxiliary stage, and in said second auxiliary stage refluxing the vapors therein with the liquid relatively poor in oxygen withdrawn from said main stage rectification and with liquid produced by liquefaction of said gas rich in nitrogen while maintaining a relatively low pressure, and finally withdrawing oxygen in the liquid phase substantially free from undesired materials from said second auxiliary stage.

4. The process of producing oxygen substantially free from undesired materials which comprises first rectifying at a relatively high pressure a liquefied gaseous mixture obtained from the atmosphere to produce material in the liquid phase relatively rich in oxygen containing any undesired high boiling point material present, then rectifying said material relatively rich in oxygen in two successive stages, in the first of which an intermediate pressure is maintained and the distillate refluxed with said material relatively rich in oxygen after it is transferred from said first rectification, while the distilled oxygen in the gas phase is withdrawn together with any low'boiling point material present and passed directly to said second stage, in said second stage refluxing with another liquid product rich in nitrogen obtained from said first rectification by withdrawing gaseous products from said first rectification and passing the same successively in heat exchanging relation with the liquid in said first and second stages, and collecting oxygen in the liquid phase substantially free from undesired materials in said second stage.

5. The process of producing oxygen substantially free from undesired materials which comprises first rectifying at a relatively high pressure a liquefied gaseous mixture obtained from the atmosphere to produce material in the liquid phase relatively rich in oxygen and containing undesired high boiling point material, collecting in conjunction with said first rectification a liquid relatively poor in oxygen, then rectifying said material relatively rich in oxygen in two successive stages, in the first of which an intermediate pressure is maintained and the distillate refluxed with said material relatively rich in oxygen in the liquid phase after it is transferred from said first rectification, while oxygen in the gas phase is withdrawn therefrom together with low boiling point material and passed directly to said second stage, in said second stage refluxing with said collected liquid relatively poor in oxygen, supplying the heat to maintain the distillations in said stages by withdrawing a gas product from said first rectification and passing the same successively in heat exchanging relation with the material being rectified in said first and second stages, supplementing the refluxing material in said second stage by passing said withdrawn gas product thereto after imparting its heat in said first and second stages, and withdrawing oxygen in the liquid phase from said second stage substantially free from undesired materials.

GEORGE J. BOSHKOFF. 

